Traditionally rigid electronics are built on ubiquitous printed circuit boards (PCB) which are neither flexible nor stretchable. Flexible electronics are, typically called flexible printed circuits (FPC), soldered on polyimide substrate which is flexible but not stretchable. Stretchable electronics, on the other hand, are printed components and/or mounting rigid components using serpentine interconnects on a stretchable substrate which is both flexible and stretchable. Potential applications for stretchable electronics are emerging such as soft robotics, energy generation and storage devices, wearable sensors, antennas, transparent conductive electrodes, and foldable/bendable OLED displays having a stretchable backplane, touch sensor and interconnects.
Current stretchable substrates are PDMS (polydimethyl siloxane) and TPU (thermal plastic urethane). TPU has hydrolytic, stability, weatherability and washability issues. PDMS has good biocompatibility, thermal stability, but is difficult to print due to poor wettability, adhesion, and surface treatment. Typical techniques for fabricating devices on elastomeric substrates entail deposition followed by lithographic patterning, deposition through a patterned shadow mask, transfer of devices by printing, and additive printing. Solvents in photolithography and printing inks may swell PDMS which results in device delamination. In addition, due to the high CTE (coefficient of thermal expansion) of PDMS, ˜300 ppm/° C., its dimensions may vary noticeably during the temperature cycles in thermal processing.
Thus, there remains a need for extruded or coextruded multilayer films suitable for use as a substrate for printed circuits that afford the simultaneous achievement of excellent mechanical properties, printability and ink curing stability, flexability and stretchability, and electronic performance. This invention achieves this, in part, by tuning the modulus of substrate using two-component blends.